Aircraft carburetor



Nov. 7, 1950 A. w. ORR, 'JR

AIRCRAFT cmsuam-oa Filid April 27, 1946 IN VEN TOR.

Patented Nov. 7, 1950 AIRCRAFT CARBURETOR Andrew William Orr, Jr, Detroit, Micln, assignor to George M. Holley and Earl Holley Application April 27, 1946, Serial No. 665,445

12 Claims. 1

The object of this invention is to control the fuel/air ratio by the quantity of air and also by the temperature and the pressure of the air flowing through a carburetor. One object is to separate the temperature responsive means from the means responsive to pressure.

9 Additional objects are to vary the enrichening fuel both as to quantity and as to the value of the main fuel flow above which it is desirable to add the enrichening fuel and to vary the idle fuel supply empirically after first temporarily 'disabling the automatic fuel/air ratio device.

This application is a continuation in part of my application Serial No. 648,301, filed February 18, 1946, now Patent No. 2,465,550, issued March 29, 1949, which in its turn was a continuation in part of my application filed April 14, 1945, Serial No. 588,359, now abandoned.

Fig. 1 shows all the essential elements of my invention.

Fig. 2 shows the position of the control valve for a normal mixture ratio, commonly known as cruising lean.

Fig. 3 shows the position of the control valve for a rich mixture.

Fig. 4 shows the position of the control valve for the idle-cut-off position.

This carburetor consists of the ordinary air flow responsive diaphragm I4 which responds to the suction in the small venturi l2 and opposes the fuel flow responsive diaphragm |5 which diaphragm responds to the drop in fuel pressure at a fuel restriction 36, fuel being supplied through the passage 30 under pressure.

When the throttle I3 is opened the airflow is out of balance and more fuel is required. This extra fuel is supplied by the servomotor valve 4| which is moved to the right and opens the valve 31, which valve has a small hole in the middle. The pipe 56 allows the pressure above the valve 31 to escape through the pipe 43. This manner of regulating fuel flow in response to an increase or decrease in air-flow is in almost universal use today for the control of the fuel/ air ratio as the air throttle |3|3 is opened'and -shut. Barometric means I6 and temperature These manual means include the throttle operated cam 96 and the fuel valve I02. vA load is simultaneously imposed on the diaphragm |4 because the spring I28 is compressed which causes the valves 4| and 31 to open.

There is also a manual means to furnish the engine with both a cruising lean and with a cruising rich mixture ratio. This consists of the manually operated shaft |22 and the two restrictions 14 and 16 in series with each other and in parallel with cruising lean fuel restriction 36. This manually operated shaft rotates the disc valve IIO- which also acts to cut off all fuel when the engine is stopped.

More specifically, in the Fig. 1, the air enters at I!) through venturi iI, flows past a small venturi l2, past a pair of throttles l3, which are geared together, and then the air passes on to the inlet of the supercharger. An air diaphragm I4 is providedwith sealing diaphragms 59 and 60 of a Well-known type, and is balanced against a fuel diaphragm IS in a well-known manner. In an equally well-known manner, a partially evacuated chamber l6 controls a valve H, which valve admits a limited amount of air at the pressure of the air entrance Ill from an annular air chamber l8 through a pipe I9 to the chamber 20 to the right hand side (suction side) of the diaphragm l4. Impact tubes 51 and drain holes 58 are provided for the reason that the full atmospheric pressure of the air entrance I0 must be applied to the left hand side of the air fiow responsive dia phragm l4. The drain holes 58 remove drops of water which would otherwise accumulate and permit the entire mechanism to freeze solid.

A passage 2| is connected to the throat of the small venturi I2 and to the passage l9 through a valve 22 which admits suction to the chamber 20 and is controlled by a diaphragm 23, a spring 24 and an opposing spring 41. At high suction in the venturi |2 there is automatically an increase in the area of the valve 22 between the pipe 2| and the passage |9. The chamber l8 communicates directly with the pressure chamber 25 to the left-hand side of the diaphragm I4. The diaphragm l4 thus responds to air flow, and the effect of air flow is corrected for changes in air density by reason of the evacuated bellows l5, which expands at high altitudes and pushes the valve down and the valve I1 is adjusted to cooperate with valve 22. High airflow causes' diaphragm 23 to rise and valve 22 increases its port area so that the Venturi suction has more and more effect on the right hand side of diaphragm l4 and thus calls for more 3 and more fuel flow. At high altitude, when the air flow approaches the critical value, there is a tendency for the mixture to become lean because the valve I'I descends so far that the pressure in chamber 20 is higher than it should be to maintain a constant fuel/ air ratio. Although the density of the air falls the velocity increases greatly and the product of velocity squared times density increases. For a given air flow measured in pounds per hour there is thus an upward movement of the diaphragm 23 at the highest altitudes. This upward movement of the valve 22 counteracts the tendency of the altitude bellows I6 to over compensate at the highest-altitudea' At moderate altitudes the bellows I6 is the major control of the fuel/air ratio and the valve 22 plays only a very minor part in the regulation of the fuel/air ratio.

My invention consists in supplementing the action of bellows I6 by means of a temperature responsive bellows 26. The openings 49 and I insure a, circulation of air around the elements I6. The openings 50 and 52 insure the circulation of air around the element. This bellows responds to the temperature variation in the air flowing through the venturi II. This feature is partially described in my previously mentioned Patent No. 2,465,550. To accomplish this there is a bulb which is located in the middle of the air stream and is connected through the pipe I2 to the bellows 26 so that at high temperature the valve 21 is in a more restricted position than it is at low temperature, at which position it is shown. The effect of high temperature is to restrict the connection through the valve 2'! between pipes 32 and 28. Pipe 32 is connected to the chamber 33. Pipe 28 is connected to the chamber 29. Hence, the pressure difference between these two chambers is reduced at low temperature and is increased at high temperature. Fuel enters at 30 and normally passes through the restriction 36 thereby creating a pressure 'drop.v Pipe 3I is connected to the fuel entrance 30 and'transmits the pressure in the fuel entrance to the chamber 29; The restricted passage 34 is connected to the chamber 35 downstream of the restriction 36. This restriction 36 is uncovered when valve H0 is in the position shown in Fig. 2. Hence, fuel flow through the passage 30 causes a pressure drop at the restriction 36 which is reflected in the two chambers 29 and 33. When the valve H0 is in the position shown in Fig. 2 the mixture ratio corresponds to a normal mixture ratio.

Valve IIO controls the ports II2, H4, H6, II8,

and I20. Rod I22 controls the position of valve .I I0. When the valve H0 is moved 40 counterclockwise into the position shown in Fig. 3 the port H4 is uncovered. In this event fuel flows.

through the two restrictions in series numbered I4 and I6. 14 is quite large relative to I6. The function of 14 is to limit the fuel added by valve I44. The area of I4 is 3 or 4 times as large as 16. I6 is relatively small as compared with 36. If the area of restriction 36 is 100 area of 14 is approximately 62 and area of I6 is approximately 20. For a given pressure drop there is a greater flow and therefore the fuel/air ratio is richer when the valve H0 is in the position shown in Fig. 3 when the ports H4 and 6- are open. When port H8 is open the chamber 35 is connected with the diaphragm chamber 33 through the restriction '34. Hence the fuel/air ratio is controlled by the temperature responsive bellows 26 and the barometric responsive element I6.

In both Figs. 2 and 3 port I20 is open. This port I20 permits high pressure fuel from the fuel entrance 30 to apply its pressure through a pipe I8. This pressure tends to unseat a valve supported by a diaphragm. This fuel that flows by the valve 80 descends past the restriction through the passage 82 to the downstream side of the throttles I3.

A chamber 88,'to the left of the diaphragm valve 80, is connected to the chamber 29 through the passage 90. A spring loaded check valve 92 admits fuel flow from the chamber, 88 to the chamber 29 but not from the chamber 29 to chamber 88. A diaphragm .94 forms the left hand wall of chamber 88.

The diaphragm 94 is operated by the cam 96 which is mounted on the shaft of the throttles I3. This cam 96 engages with a lever 98 which in turn engages with the diaphragm 94 so that when the throttles are open the diaphragm 94 moves to the left lowering the pressure in the chamber 88 and permits the valve 80 to move to the left. This provides a small quantity of fuel for acceleration purposes. A restricted passage I00 provides communication between the chamber 88 and the pipe 18. This port I20 is open in Figs. 2 and 3 and is closed in Fig. 4 which is the idle-cut-off position.

A low speed valve I02 controls the flow at low'speed when the throttles I3 approach the closed position. Valve I02 restricts the flow from the chamber 35 to the passage 38. The perforated valve 31 supported by the diaphragm 42 and seated by the compression spring 45 regulates the flow from the chamber 35 to the passage 38. This regulation is accomplished by the servo-valve M and the passages 43 and 56. Passage 56, when the diaphragm I5 moves to the right, is in free communication with the passage 43 so that the only force seating the valve 31 is the compression spring 45. The pressure acting upwards on the diaphragm 42 is the pressure in the outlet passage 38 which fuel pressure is lower than the pressure in chamber 35. This low pressure acting through the passages 56 and 43 and valve 4I (when open) reduces the pressure above the diaphragm 42 and counteracts the effect of the perforation in themiddle of the valve 31 which admits high pressure to the upper side of the diaphragm 42. The valve 31 rises and fuel flows by the valve 31 to the fuel outlet 40 past the valve 39. The valve 39 is supported by the diaphragm 55 and the spring 53 tends to open the valve 39.

Chamber 54, to the right of the diaphragm 55, is connected through the pipe I04 to the fuel entrance 30. The diaphragm I06, to the right of chamber 54, forms the left hand wall of the air chamber I08 which is connected to the air entrance I0. A compression spring I24 in the chamber I 08 supports the fuel pressure in the chamber 54 and supports the right hand side of the diaphragm I06.

The idle spring I28 adds a force additional to that of the venturi throat differential pressure across diaphragm l4. This additional force increases the fuel diiferential across the main fuel metering jets 14, I6 and 36; the fuel flow is now decreased by the restriction imposed by the idling valve I02 which restriction is in series with the jets 14, I6 and 36. The combination of these two elements, the spring I28 and the valve I02, provides the carburetor with the desired fuel/air ratios. In the low cruising and all higher power 5 ranges both of these elements are almost completely removed from action.

When in the normal lean position port H2 is open. When in the rich position this port H2 is closed. This port II2 communicates with the chamber I34 through a restriction I38. A diaphragm I38 forms the right hand wall of the chamber I34 which chamber is connected through the passage I40 through the restriction I42 with the fuel entrance 30. An enrichening valve I44 is provided so that when the fuel flow exceeds a predetermined value then the drop in pressure downstream from the fuel restriction 36 (resulting from the predetermined fuel flow) causes the fuel/air ratio to depart from the constant value established by the opposing air and fuel diaphragms, the servomotor valve 4| and the valve 31, controlled by this servomotor valve 4I.

The valve I44 is controlled by the diaphragm I38. Valve I44 is seated by the spring I48 and by the low pressure existing in the chamber I34. The chamber I48, to the right hand side of the diaphragm I38, is connected to the downstream side of restriction 38.

Operation When the port H2 is open (Fig. 2 cruising lean) then the pressure in I34 is low and the opening of the valve (the enrichening valve) is delayed. However when valve I44 does open it opens quickly as the pressure drop through the single restriction 36 is greater than through the multiple restrictions 36, 14 and 16 (Fig. 3 cruising rich) because the restrictions 14 and I6 are in parallel with the restriction 36. It follows that although the enrichening valve opening is delayed by a low pressure in chamber I34 (Fig. 2) when it does open it makes up for lost time so that the ultimate mixture ratio at maximum air fiow is the same both for cruising lean (Fig. 2) and cruising rich (Fig. 3).

The fact that restriction I4 feeds the fuel enrichening valve I44 when the mixture control I I is in the lean position (Fig. 2) and feeds both I44 and the enrichening restriction 16 when the mixture control H0 is in the rich position (Fig. 3) means that the flow through 38 plus fiow through 14 is the maximum fuel flow, so that the maximum attainable fuel flow is the same whether valve III) is in rich or lean position, that is, in Fig. 3 or Fig. 2 position. When the throttle is moved towards its closed position the cam 96 gradually closes the valve I02 and also imposes a spring load (I28) on the diaphragms I4-I5 so that the servomotor valve H is opened and the pressure above and below the diaphragm 42 is equalized. The valve 31 is opened by the pressure in chamber 35 and the fuel flow is controlled by the restricted area past the low speed fuel valve I02. During the transition period, between empirical and automatic control, both the diaphragms gradually take over the control of the fuel flow as the valve I02 moves into its wide open, that is, into its inoperative position.

One or more of the following elements, barometric element I6, thermostatic elements 10 and 26, air flow responsive elements 22 and 23, can be dispensed with especially when the carburetor is applied to a, marine engine. In that event the diaphragm I4 responds to the difference in suction between the air entrance I0 and the throat of the venturi I2, also the diaphragm I5 responds to the drop in pressure across the restriction 36 when the control is in the position 6. shown in Fig. 2 and to the drop across restrictions 36 and I6 when the control is in the position shown in Fig. 3.

What I claim is:

1. In a carburetor having an air entrance and a venturi therein, an air chamber, an air diaphragm dividing the air chamber into two halves, a passage connecting the throat of said venturi to a low pressure side of said diaphragm, an automatic valve normally unseated and located in said passage adapted to be further opened by an increase in venturi suction, a second passage connecting the low pressure side of the diaphragm to the air entrance, a barometric responsive valve in said second passage, said valve being responsive to pressure of the air in the air entrance and being adapted to admit more air at air entrance pressure into the .low pressure side of said diaphragm as the pressure in the air entrance decreases, a passage transmitting the air entrance pressure to the high pressure side of the air diaphragm, a fuel chamber, a diaphragm therein, dividing the fuel chamber into two halves, said diaphragm being arranged to oppose the movement of the air diaphragm, a fuel entrance, a fuel passage, a fuel restriction therein, a passage connecting the pressure side of said fuel diaphragm with the pressure on the upstream side of said fuel restriction, a passage connecting the low pressure side of said fuel diaphragm with the downstream side of said fuel restriction, an automatic fuel control valve, means inter-connecting the air and fuel diaphragms with said automatic fuel control valve so as to vary the fuel flow and maintain the two diaphragms in equilibrium so as to maintain a fuel/air ratio at an approximately constant value, a bypass from the high pressure side to the low pressure side of said fuel diaphragm, a valve in said bypass, a temperature responsive element connected to said valve being located so as to respond to the mean temperature of the air flowing through the air entrance, said temperature responsive valve being adapt/ed to be moved to a relatively less restricted position at low temperature and to a relatively more restricted position at high temperature.

2. A device as set forth in claim 1 in which there is a mixture control valve and a second fuel passage in parallel with the first fuel passage and having a second fuel restriction therein quite small compared with the first mentioned fuel restriction, said second restricted fuel passage being adapted to be opened by said mixture control valve so as to give a somewhat richer mixture than when the first restricted fuel passage is used alone.

3. A device as set forth in claim 1 in which there is a bypass around the first mentioned fuel restriction, an automatic enrichening valve in said bypass, a third diaphragm operatively connected to said enrichening valve on the downstream side thereof, a chamber on the opposite side of said third diaphragm, an increase of pressure in said chamber being adapted to open said valve, means for varying the pressure in this chamber comprising a restricted bypass leading from the fuel entrance around said first mentioned fuel restriction and connecting with this said chamber associated with this third diaphragm, a port for varying the flow through said bypass, a second main fuel passage and a second fuel restriction in parallel with the first mentioned restriction, said second fuel restriction 7 being small compared with the first mentioned fuel restriction, a mixture control valve adapted when in the rich position to simultaneously open the second fuel passage and second fuel restriction therein and to control the port in said third diaphragm bypass so as to increase the pressure in the chamber on the valve opening side of said I third diaphragm whereby the enrichening valve is caused to open at a less pressure difference across the first mentioned fuel restriction than when the mixture control is in its lean position so that the mixture begins to get richer than that given by the automatic means at a lower pressure difference when the control is in the rich position and the mixture stays leaner for greater fuel fiows when the control is in its lean position.

4. In a device as set forth in claim 1 in which there are idling means to override the normal mixture ratio control means comprising mechanism operated by the throttle as the throttlev approaches the idling position, to impose a yieldable load on the pressure side of the air diaphragm so as to increase the fuel fiow and an additional fuel restriction inserted in series with the first mentioned fuel restriction so as to positively control the resulting increased fuel flow.

5. In a carburetor having an air entrance and a double venturi therein, an air chamber, an air diaphragm dividing the air chamber into two halves, a passage connecting the throat of said venturi to a low pressure side of said diaphragm, an automatic valve normally unseated and located in said passage adapted to be further opened by an increase in venturi suction, a second passage connecting the low pressure side of the diaphragm to the air entrance, a barometric responsive valve in said second passage, said valve being responsive to pressure of the air in the air entrance and being adapted to admit more air at air entrance pressure into the low pressure side of said diaphragm as the pressure in the air entrance decreases, a passage transmitting the air entrance pressure to the high pressure side of the air diaphragm, a fuel chamber, a diaphragm therein, dividing the fuel chamber into two halves, said diaphragm being arranged to oppose the movement of the air diaphragm, a fuel entrance, a fuel passage, a fuel restriction therein, a passage connecting the pressure side of said fuel diaphragm with the pressure on the upstream side of said fuel restriction, a passage connecting the low pressure side of said fuel diaphragm with the downstream side of said fuel restriction, an automatic fuel control valve, means inter-connecting the air and fuel diaphragms with said automatic fuel control valve so as to vary the fuel [low and maintain the two diaphragms in equilibrium so as to maintain a fuel/air ratio at an approximately constant value, idling means to override the normal mixture ratio control means comprising mechanism operated by the throttle as the throttle approaches the idling position, to impose a yieldable load on the pressure side of the air diaphragm so as to increase the fuel flowand an additional fuel restriction inserted in serles with the first mentioned fuel restriction so as to positively control the resulting increased fuel fiow.

6. In a carburetor having an air entrance and a double venturi therein, an air chamber, an air diaphragmdividing the air chamber into two halves, a passage connecting the throat of aid venturi to a low pressure side of said diaphragm, an automatic valve normally unseated and located in said passage adapted to be further opened by an increase in' venturi suction, a second passage connecting the low pressure side of the diaphragm tothe air entrance, a baremetric responsive valve in said second passage, said valve being responsive to pressure of the air in the air entrance and being adapted to admit more air at air entrance pressure into the low pressure side of said diaphragm as the pressure in the air entrance decreases, a passage transmitting the air entrance pressure to the high pressure side of the air diaphragm, a fuel chamber, a diaphragm therein, dividing the fuel chamber into two halves, said diaphragm being arranged to oppose the movement of the air diaphragm, a fuel entrance, a fuel passage, a fuel restriction therein, a passage connecting the pressure side of said fuel diaphragm with the pressure on the upstream side of said fuel restriction, a passage connecting the low pressure side of said fuel diaphragm with the downstream side of said fuel restriction, an automatic fuel control valve, means inter-connecting the air and fuel diaphragms with said automatic fuel control valve so as to vary the fuel flow and maintain the two diaphragms in equilibrium so as to maintain a fuel/air ratio at an approximately constant value, a bypass around the first mentioned fuel restriction, an automatic enrichening valve in said bypass, a third diaphragm operatively connected to said enrichening valve on the downstream side thereof, a chamber on the opposite side of said third diaphragm, an increase of pressure in said chamber being adapted to open said valve, means for varying the pressure in this chamber comprising a restricted bypass leading from the fuel entrance around said first mentioned fuel restriction and connecting with this said chamber associated with this third diaphragm, a port for varying the flow through said bypass, a second main fuel passage and a second fuel restriction in parallel with the first mentioned restriction, said second fuel restriction being small compared with the first mentioned fuel restriction, a mixture control valve adapted when in the rich position to simultaneously open the second fuel passage and second fuel restriction therein and to control the port in said third diaphragm bypass so as to increase the pressure in the chamber on the valve opening side of said third diaphragm whereby the enrichening valve is caused to open at a less pressure difference across the first mentioned fuel restriction than when the mixture control is in its lean position so that the mixturebegins to get richer than that given by the automatic means at a lower pressure difference when the control is in the rich position and the mixture stays leaner for greater fuel flows when the control is inits lean position.

7. In carburetor having an air entrance and a double venturi therein, an air chamber, an air diaphragm dividing the air chamber into two halves, a passage connecting the throat of said venturi to a low pressure side of said diaphragm, an automatic valve normally unseated and located in said passage adapted to be further opened by an increase in venturi suction, a second passage connecting the low pressure side of the diaphragm to the air entrance, a barometric responsive valve in said second passage, said valve being responsive to pressure of the air in the air entrance and being adapted to admit more air at air entrance pressure into the low pressure side of said diain, dividing the fuel chamber into two halves,

said diaphragm being arranged to oppose the movement of the air diaphragm, a fuel entrance, a fuel passage, a fuel restriction therein, a passage connecting the pressure side of said fuel diaphragm with the pressure on the upstream side of said fuel restriction, a passage connecting the low pressure side of said fuel diaphragm with the downstream side of said fuel restriction, an automatic fuel control valve, means inter-connecting the air and fuel diaphragms with said automatic fuel control valve so as to vary the fuel flow and maintain the two diaphragms in equilibrium so as to maintain a fuel/air ratio at an approximately constant valve, a bypass around the first mentioned fuel restriction, a

second restriction therein somewhat smaller than the first mentioned restriction, an automatic enrichening valve arranged in said bypass downstream from said second restriction, a third diaphragm operatively connected to said automatic enrichening valve on the downstream side thereof, a chamber on the opposite side of said third diaphragm, yielding means adapted to close said valve, an increase of pressure in said chamber being adapted to open said valve, means for maintaining a pressure in said chamber intermediate between the pressures above and below the first mentioned restriction comprising a restricted bypass leading from the fuel entrance to the downstream side of first mentioned fuel restriction, and connected with the said chamber, the opposite side of said diaphragm from said chamber being in free communication with the downstream side of said valve and of said first mentioned restriction, whereby the valve is opened when the drop in pressure across said first mentioned restriction increases and a considerable quantity of fuel is admitted but less than that admitted through the first mentioned restriction because the second fuel restriction is smaller than the first mentioned restriction.

8. In a carburetor having an air entrance and a double venturi therein, an air chamber, an air diaphragm dividing the air chamber into two halves, a passage connecting the throat'of said venturi to a low pressure side of said diaphragm, an automatic valve normally unseated and located in said passage adapted to be further opened by an increase in venturi suction, a second passag connecting the low pressure side of the diaphragm to the air entrance, a barometric responsive valve in said second passage, said valve being responsive to pressure of the air in the air entrance and being adapted to admit more air at air entrance pressure into the low pressure side of said diaphragm as the pressure in the air entrance decreases, a passage transmitting the air entrance pressure to the high pressure side of the air diaphragm, a fuel chamber, a diaphragm therein, dividing the fuel chamber into two halves, said diaphragm being arranged to oppose the movement of the air diaphragm, a fuel entrance, a fuel passage, a fuel restriction therein, a passage connecting the pressure side of said fuel diaphragm with the pressure on the In upstream side of said fuel restriction, a passage connecting the low pressure side of said fuel diaphragm with the downstream side of said fuel restriction, an automatic fuel control valve,

means inter-connecting the air and fuel dia- 75 phragms with said automatic fuel control valve so as to vary the fuel flow and maintain the two diaphragms in equilibrium so as to maintain a fuel/air ratio at an approximately constant value, a second fuel supply passage in parallel with the first mentioned fuel restriction, a second and a third restriction in series in'said second passage, the second restriction being upstream from the third and the second fuel restriction being between 50% and of the area of the first mentioned restriction and the third restriction being between 10% and 30% of the area of the first mentioned restriction, a passage leading out of the second passage between the second and third restriction to the downstream side of said first mentioned fuel restriction, an automatic valve in said passage, means responsive to the pressure drop across first mentioned fuel restriction to open said automatic valve yieldable means opposing said opening, mixture control means for simultaneously closing the outlet from the third restriction and increasing the pressure drop across the first mentioned restriction necessary to open said automatic valve. 9. In a carburetor having an air entranc an a double venturi therein, an air chamber, an air diaphragm dividing the air chamber into two halves, a passage connecting the throat of said venturi to a low pressure side of said diaphragm, a passage transmitting the air entrance pressure to the high pressure side of the air diaphragm, a fuel chamber, a diaphragm therein, dividing the fuel chamber into two halves, said diaphragm being arranged to oppose the movement of the air diaphragm, a fuel entrance, a fuel passage, a fuel restriction therein, a passage connecting the pressure side of said fuel diaphragm with the pressure on the upstream side of saidfuel restriction, a passage connecting the low pressure side of said fuel diaphragm with the downstream side of said fuel restriction, an automatic fuel control valve, means inter-connecting the air and fuel diaphragms with said automatic fuel control valve so as to vary the fuel fiow and maintain the two diaphragms in equilibrium so as to maintain a fuel/air ratio at an approximately constant value, a bypass around the first mentioned fuel restriction, an automatic enrichening valve in said bypass, a third diaphragm operatively connected to said enrichening valve on the downstream side thereof, a chamber on the opposite side of said third diaphragm, an increase of pressure in said chamber being adapted to open said valve, means for varying the pressure in this chamber comprising a restricted bypass leading from the fuel entrance around said first mentioned fuel restriction and connecting with this said chamber associated with this third diaphragm, a port for varying the flow through said bypass, a second main fuel. passage and a second fuel restriction in parallel with the first mentioned restriction, said second fuel restriction being small compared with the first mentioned fuel restriction, a mixture control valve adapted when in the rich position to simultaneously open the second fuel passage and second fuel restriction therein and to control the port in said third diaphragm bypass so as to increase the pressure in the chamber on the valve opening side of said third diaphragm whereby the enrichening valve is caused to open at a less pressure difference across the first mentioned fuel restriction than when the mixture control is in its lean position so that the mixture begins to get richer than that given by the automatic means at a lower and a double venturi therein, an air chamber, an air diaphragm dividing the air chamber into two halves, a passage connecting the throat of said venturi to a low pressure side of said diaphragm, an automatic valve normally unseated and located in said passage adapted to be further opened by an increase in venturi suction, a passage transmitting the air entrance pressure to l the high pressure side of the air diaphragm, a

fuel chamber, a diaphragm therein, dividing the fuel chamber into two halves, said diaphragm being arranged to oppose the movement of the air diaphragm, a fuel entrance, a fuel passage, a fuel restriction therein, a passage connecting the pressure side of said fuel diaphragm with the pressure on the upstream sideof said fuel restriction, a passage connecting the low pressure side of said fuel diaphragm with the downstream side of said fuel restriction, an automatic fuel control valve, means inter-connecting the air and fuel diaphragms with said automatic fuel control valve so as to vary the fuel flow and maintain the two diaphragms in equilibrium so as to maintain a fuel/air ratio at an approximately constant value, a second fuel supply passage in parallel with the first mentioned fuel restriction a second and a third restriction in series in said second passage, the second restriction being upstream from the third and the second fuel restriction being between 50% and 70% of the area of the first mentioned restriction and the third restriction being between and 30% of the area of the first mentioned restriction, a passage leading out of the second passage between the second and third restriction to the downstream side of said first mentioned fuel restriction, an automatic valve in said passage, means responsive to the pressure drop across first mentioned fuel restriction to open said automatic valve yieldable means opposing said opening, mixture control means for simultaneously closing the outet from the third restriction and increasing the pressure dropacross the first mentioned restric-' tion necessary to open said automatic valve.

11. In a carburetor having an air entrance and a double venturi therein, an air chamber, an air diaphragm dividing the air chamber into two halves, a passage connecting the throat of said venturi to a low pressure side of said diaphragm, an automatic valve normally unseated and located in said passage adapted to be further opened by an increa e in venturi suction, a passage transmitting the air entrance pressure to the high pressure side of the air diaphragm, a fuel chamber. a diaphragm therein, dividing the fuel chamber into two halves. said diaphragm being arranged to oppose the movement of the air diaphragm, a fuel entrance, a fuel pas age, a fuel restriction therein. a passage connecting the pressure side of said fuel diaphragm with the pressure on the upstream side of said fuel restriction, a passage connecting the low pressureside of said fuel diaphragm with the downstream side of said fuel restriction, an automatic fuel control valve, means interconnecting the air and fuel diaphragms with said automatic fuel control valve so as to vary the fuel fiow and maintain the two diaphragms in equilibrium so as to maintain a fuel/air ratio at an approximately constant value. a bypass around the first mentioned fuel said third diaphragm, yielding means adapted to 1 close said valve, an increase of pressure in said chamber being adapted to open said valve, means for maintaining a pressure in said chamber intermediate between the pressures above and below the first mentioned restriction comprising a restricted bypass leading from the fuel entrance to the downstream side of first mentioned fuel restriction, and connected with the said chamber, the opposite side of said diaphragm from said chamber being in free communication with the downstream side of said valve and of said first mentioned restriction, whereby the valve is opened when the drop in pressure across said first mentioned restriction increases and a. considerable quantity of fuel is admitted but less than that admitted through the first mentioned restruction because the second fuel restriction is smaller than the first mentioned restriction.

12. In a carburetor having an air entrance and a double venturi therein, an air chamber, an air diaphragm dividing'the air chamber into two halves, a passage connecting the throat of said venturi to a low pressure side of said diaphragm, an automatic valve normally unseated and lo cated in said passage adapted to be further opened by an increase in venturi suction, a passage transmitting the air entrance pressure to the high pressure side of the air diaphragm, a fuel chamber, a diaphragm therein, dividing the fuel chamber into two halves, said diaphragm being arranged to oppose the movement of the air diaphragm. a fuel entrance, a fuel passage, afuel restriction therein, a passage connecting the pressure side of said fuel diaphragm with the pressure on the upstream side of said fuel restriction, a passage connecting the low pressure side. of said fuel diaphragm with the downstream side of said fuel restriction, an automatic fuel control valve, means inter-connecting the air and fuel diaphragms with said automatic fuel control valve so as to vary the fuel fiow and maintain the two diaphragms in equilibrium so as to maintain a fuel/air ratio at an approximately constant value, a bypass around the first mentioned fuel restriction, an automatic enrichening valve in said bypass, a third diaphragm operatively connected to said enrichening valve on the downstream side thereof, a chamber on the opposite side of said third diaphragm, an increase of pressure in said chamber being adapted to open said valve, means for varying the pressure in this chamber comprising a restricted bypass leading from the fuel entrance around said first mentioned fuel restriction and connecting with this said chamber associated with this third diaphragm, a port for varying the flow through said bypass, a second main fuel passage and a second fuel restriction in parallel with the first mentioned restriction, said second fuel restriction being small compared with the first mentioned fuel restriction. a mixture control valve adapted when in the rich position to simultaneously open the second fuel passage and second fuel restriction therein and to control the port in said third diaphragm bypass so as to increase the pressure in the chamber on the valve opening side of said diaphragm whereby the enrichening valve is 13 l4 caused to open at a less pressure difference across REFERENCES CITED the first mentioned fuel restriction than when The following references are of record in the the mixture control is in its lean position so that the mixture begins to get richer than that given file of thls patent by the automatic means at a lower pressure dif- 5 UNITED STATES PATENTS Ierence when the control is in the rich position Number Name Date and the mixture stays leaner for greater fuel 2,361,227 Mock Oct. 24, 1944 flows when the control is in its lean position. 2,3 7,499 Holley, Jr Jan. 16, 1945 2,378,036 Reggio June 12, 1945 ANDREW WILLIAM ORR, Jr. 10 2,394,664 Chandler Feb. 12, 1946 2,417,304 Kittler et a1 Mar. 11, 1947 2,442,046 Hunt May 25, 1948 

